Accolon

In Malory's Le Morte D'Arthur, when King Arthur entrusted Excalibur into Morgan le Fay's care, she had a duplicate made; the real scabbard was then passed from her to her lover Accolon.Morgan then tricked Arthur and Accolon into fighting each other, Accolon using the real Excalibur while Arthur used the duplicate. During the battle Arthur's sword broke; he quickly realized this was not the real Excalibur and that he had been betrayed. Rather than giving up, Arthur continued to fight with what was left of his shield. Nimue, the Lady of the Lake, arrived and used her magic to cause Excalibur to fly from Accolon's hand. Arthur then wrestled it back and dealt Accolon a mortal wound. Accolon died four days after receiving the battle-wound from Arthur.
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[Arthurian] Paramour of Morgan le Fay. First appearing in an expansion of De Boron's Merlin, Malory then picks up his tale. Morgan steals Excalibur, gives it to Accolon and leaves a non-magical replica in its stead. Arthur, sensing the deception, recovers his sword and defeats Accolon in battle.